The Magic of Slushie Machines

Did you know that making a slushie involves some chemistry and physics? Try taking the temperature of a slushie when it is fresh out of the machine sometime. Water freezes at 32 degrees, but if you measure the temperature of a slushie it’s actually around 26-27 degrees. This seems impossible, but it’s not if you know the tricks. Half the magic comes from the slushie mix. The other half comes from the machine’s design. It’s a pretty ingenious device if you stop to think about it.

Slushies are a mixture of water, sugar, flavoring, and coloring. Slush mix has to be cold enough to form enough ice crystals to become a slush, but not so cold that you get one big block of ice. When sugar is added to water, it lowers the freezing temperature of water. How does it do it? For ice to form, water molecules have to be cold enough and they have to touch. Sugar molecules are quite large. They form barriers between the water molecules to keep it from freezing so easily.

The ratio of sugar to water in the slushie machine is quite important. If there is more than 22% sugar in the mixture, the refrigeration unit won’t get the mixture cold enough to freeze into slush. You’d just get very cold sugar water. If there is less than 12%, then there’s not enough sugar and the mix will freeze into a block of ice. If this happens, your unit will be damaged. That’s why it’s very important to have your mix ratios correct.

If sugar is the main thing keeping the mix from freezing, why do we need a slushie machine then? If you take apart a slushie machine, there are three main units. There is a refrigeration unit, a mixing unit, and a dispensing unit. The refrigeration unit keeps the bowl very cold on the bottom, and the dispensing unit holds the mix until it’s needed. If you were to cool a glass of water from the bottom, eventually a layer of ice would form that would float to the top. That’s not good for a slushie though. We want small pieces of ice throughout the mixture.

That’s what the mixing unit is for. The two mixers in a slush machine move the mix vertically and horizontally to evenly cool the mix. It also keeps the mixture flowing past the cold part at the bottom at a rate that doesn’t allow large ice crystals to form. This constant churning of the mix and the motion from the cold bottom to the warmer top gives slushies that smooth texture.

Through these two little tricks, we can enjoy slushies with just enough ice at the right consistency. Now if you have a customer ask how the machine works, now you know!